As-CAST, RARE-EARTH-Co-Cu PERMANENT MAGNET MATERIAL

ABSTRACT

Permanent magnet material having a high coercive force and a high residual flux density is constituted by an alloy of cerium (15 to 20 mol percent), cobalt (52 to 77 mol percent) and copper (8 to 30 mol percent). The cerium can be replaced by Cemischmetal in an amount providing the equivalent quantity of cerium. The material has a novel microstructure. The material can be prepared by melting together the ingredient materials and furnace-cooling to room temperature. Superior results are obtained with specially scheduled heat-treatments including controlled cooling rates. It is not necessary to use fine particle magnet material.

ilnited tates Patent [191 Tawara et a1.

[451 Feb. 5, 1974 1 1 AS-CAST, RARE-1E 1% TH-CO-CU PERMANENT MAGNET MATEAL [75] Inventors: Yoshio Tawara; liiaruiumi Senno,

both of Osaka, Japan [22] Filed: Nov. 14, 1968 [21] Appl. No.: 775,651

[30] Foreign Application Priority Data Nov. 15, 1967 Japan 42-74374 Feb. 8, 1968 Japan 43-13233 Mar. 18, 1868 Japan 43-18152 Mar. 18, 1968 Japan 43-18153 Mar. 18, 1968 Japan 43-18154 [52] US. Cl 148/3157, 75/84, 75/170, 148/101,148/102,148/103 [51] Int. Cl C041) 35/00 [58] Field of Search 75/123, 152, 170, 84; 148/3157, 101, 102,103,105

[56] References Cited UNITED STATES PATENTS 2,813,789 11/1957 Glaser 75/123 3,102,002 8/1963 Wallace et a1. 75/152 X 3,421,889 1/1969 Ostertag et a1. 75/152 X 3,424,578 1/1969 S trnat et a1. ..7"5/2'1'3 3,501,358 3/1970 Becker 148/3157 X 3,523,836 8/1970 Buschow et a] 75/170 X 3,546,030 12/1970 Buschow et a1 148/3157 3,560,200 2/1971 Nesbitt et a1. 75/122 FOREIGN PATENTS OR APPLICATIONS 6,608,335 12/1967 Netherlands 148/3157 OTHER PUBLICATIONS Stmat, K. et al., A Family of New Cobalt-Base Permanent Magnet Materials, Jouma1 of Applied Physics, Vol. 38, No. 3, March, 1967, pages 1001 and 1002.

Velge, W. A. J. J. et al., Magnetic and Crystallographic Properties of Some Rare Earth Cobalt Compounds with CaZn, Structure, Journal of Applied Physics, Vol. 39, No. 3, February, 1968, pages 1717-1720.

Primary ExaminerL. Dewayne Rutledge Assistant Examiner-W. R. Satterfield Attorney, Agent, or Firm-Wenderoth, Lind &. Ponack [57] ABSTRACT Permanent magnet material having a high coercive force and a high residual flux density is constituted by an alloy of cerium (15 to 20 mol percent), cobalt (52 to 77 mol percent) and copper (8 to 30 mol percent). The cerium can be replaced by Ce-mischmetal in an amount providing the equivalent quantity of cerium. The material has a novel microstructure. The material can be prepared by melting together the ingredient materials and fumace-cooling to room temperature. Superior results are obtained with specially scheduled heat-treatments including controlled cooling rates. It is not necessary to use fine particle magnet material.

6 Claims, 4 Drawing Figures PNENFEU BJQOAlfl MN 3 UF 4 FIG.

ueuntoeds o ssrnqeladmaq YOSHIO TAWARA & ILARUFUMI SENNO,

Inventors mum PNEMEB FEB W SHEEY a (1F Q A s 95mm 0) e010; a qroxeog Inventors [\Ltormgyg YOSIIIO TAWARA & HARUFUMI SENNO,

AS-CAST, RARE-EARTH-CO-CU PERMANENT MAGNET MATERIAL This invention relates to a permanent magnet mateis a Ce-rich metal and is widely used in industry because of the lower cost than that of pure Ce metal. As is well known, the Ce-mischmetal contains, as a main ingredient, Ce, rare earth metals such as La, Pr and Nd rial characterized by a high coercive force and a 5 in a small amount, and other metals such as Fe, Mg and residual flux density and to a manufacturing method A] in a very small amount. thereof. Ce-mischrnetal, in the present specification, refers to It has been suggested that the alloy composed of a an alloy having a composition according to Table l.

w Tagle .1.

Ce La Pr ND other rare Fe Mg Al earth metal Ce-mischmetal 40-94 3-30 01-4 0.l-l.5 0.1-1.0 0.1-8.0 -1.0 04.0

rare earth metaland a transition metal such as YCo is a promising candidate for a fine particle magnet material. It has been a problem, however, how to make a fine and chemically stable particle of the material. In general, a mechanically crushed particle of the material is liable to be oxidized in air and the oxidation is accelerated by the coexistence of moisture even at room temperature. Therefore, it is desired to make a magnet of the material without using the pulverized form thereof.

An object of the invention is to provide a novel magnetic material characterized by a high coercive force and a high residual flux density.

A further object of the invention is to provide a permanent magnet material comprising Ce, Co and Cu.

A still further object of the invention is to provide a composition of the alloy consisting of Ce, Co and Cu,

which gives a high coercive force, without pulverizing the alloy.

A further object of the invention is to provide a permanent magnet material comprising Ce-mischmetal in- These and other objects which are achieved by the;

present invention will be apparent upon consideration of the following detailed description taken together with the accompanying drawings wherein:

FIG. I is a schematic drawing which shows a structure, enlarged by 200 times, of the alloy according to the present invention;

FIG. 2 shows the relation between the intrinsic coercive force in oersteds and the fineness of the fiber-like structure in microns, which is characteristic of the alloy of the present invention;

FIG. 3 shows an example of cooling rate applicable to the method of manufacturing the magnet material of the invention;

7 H FIG. 4is a graph showing the relation between the intrinsic coercive force and the aging timeaccording to one example of the invention.

According to the present invention, an alloy which consists of proper amounts of Ce, C0 and Cu has excellent magnetic properties for use as a permanent magnet. A novel composition of ferromagnetic alloy according to the invention comprises to mol percent of Ce, 52 to 77 mol percent of Co and 8 to mol percent of Cu. The 15 to 20 mol percent of Ce can be replaced by the less expensive Ce-mischmetal without impairing the magnetic properties. The Ce-mischmetal Thlflib' specimens of the present inventiori'have an interesting microstructure which has not been found in any Brie? similar magnetic arra consisting bf" any other combination of rare earth metals and transition metals. The microstructure consists of a fiber-like structure as shown in FIG. 1. It is observed with a conventional microscope on the fiat surface of specimens etched by conc. HCl for a few minutes. It has been discovered that a high coercive force is closely related to the microstructure. In a specimen having a high coerciveforce, quite definite and fine fiber structure are found, whereas, in a specimen with 510w coercive force, such a structure as above mentioned is hardly found.

The alloy body of the invention as heated is polished at one surface thereof with a suitable abrasive such as SiC powder or Cr O powder in a particle size of 0.5 to 10a in order that it may be provided with a flat surface. The surface is etched by a 12N HCl solution (aqueous) for several minutes at room temperature (15 to 30C). The etched surface shows an etch pattern when observed microscopically as shown in FIG. I. Said etch pattern is composed of many etch fibers 2,

with a characteristic fineness defined as the average distance between two adjacent points 4 and 6 on a straight line 3 taken on the etch pattern, crossed by the etch fibers. In order to determine the fineness of the fiber-like structure, it is convenient to measure the same on a microscopic photograph. It can be made by drawing a sufficiently long straight line on the microscopic photograph in an arbitrary directiofif so t liat there will be many cross points of the line with the etch fibers. The average distance is obtained by dividing the line length by the number of all such cross points on the line.

According to the present invention, the smaller the fineness of the alloy. the higher the coercive force thereof. The alloy having a fineness larger than 100a has a poor coercive force such as lower than 500 Oe regardless of the composition. A coercive force higher than 2,000 Oe is obtained with an alloy having a fineness smaller than 20g. FIG. 2 shows the relation between intrinsic coercive force and the fineness of the fiber-like structure of various specimens of the invention. It is clearly seen from FIG. 2 that the finer the structure the higher is the coercive force.

The alloy according to the present invention with the aforedescribed structure was crushed to a fine particle size and examined by X-ray powder diffractometry. An example of the analysis for the alloy having a composition of 16.7 mol Ce, mol Co and 8.3 mol Cu is shown in Table 2. In the measurement, Fe-Ka radiation generated in an X-ray tube working at an anode voltage of 35 kV and an anode current of 8 mA through a Mn filter was used as X-ray source. The diffracted Xray from the specimen was counted by a conventional counter at a counting rate of 400 c/s and a scanning velocity of 1 /min. and recorded at a time constant of 2 sec.

"uk. unknown, w weak, m medium,

.r strong, .rs very strong The observed diffraction angles, 20, are listed in the first column ofTable 2. 1n the second column, is shown the line intensity. The interplanar spacings [d] corresponding to each line are shown in the third column. Some of the diffraction lines can be indexed as shown in the fourth column, assuming that the crystal phase has a CaCu -type structure which is well verified in the case of many RC compounds. The other lines, however, remain unexplained. The most intense ones among the unexplained lines appear at slightly lower angles than the main lines of (111) and (110). This looks like a splitting of the main line into two lines. Although the origin of these extra lines are unknown at present, it should be noted that these lines are characteristic of the alloy of the present invention.

The materials according to the present invention have a residual flux density higher than 3,500 G, a coercive force higher than 600 Oe, and a maximum energy product higher than 1.3 MG'Oe. The best results are obtained with compositions consisting essentially of 17.1 to 17.4 mol percent of Ce, 64 to 72.6 mol percentgof Co and 10.3 to 18.57 mol percent of Cuin which the fine fiber-structure is easily formed. It is possible to replace Ce with Ce-mischmetal so that the amount of total rare earth elements in said Ce-mischmetal is equivalent to that of said Ce, without impairing the resultant magnetic properties. The material of said optimal composition with a markedly developed fiberstructure has a residual flux density higher than 4,250 G, a coercive force higher than 1,500 Oe, and a maximum energy product higher than 4.0 MG'Oe.

The magnetic alloys according to the invention can be prepared by a conventional metallurgical method. For example, the ingredient metals are melted together in an alumina crucible in air at mmHg using a graphite heater, and the. molten alloy is furnace-cooled to room temperature. The alloy thus prepared has a more or less developed fiber-structure. However, in order to obtain a clearly and finely developed fiberstructure with tlie alloy materials and accordingly a high coercive force, it is effective to give the materials specially scheduled heat-treatments.

According to one manufacturing method of the pres ent invention, the mixed ingredient metalsare melted at a temperature higher than 1,200C, said melt is solidified at a temperature slightly lower than the melting point of the desired alloy, the solidified alloy is maintained at a temperature between the solidifying temperature and about 1,000C to obtain a homogenized alloy, the homogenized alloy is cooled to a temperature of 650 to 250C at an average rate of 35 to 3C per minute, and then the resultant alloy is quenched to room temperature. The homogenizing treatment, although not necessary, has a favorable effect on the magnetic properties.

An important feature of the process is the controlled colli ng after the homogenizing heat treatment in order to obtain superior magnetic properties. The magnetic properties are highly dependent on the said cooling rate from 1,100C to 250C.

The cooling rate should be higher in a relatively high temperature region than in a relatively low temperature region. The mostim portant process featureis the controlled colling from 1,000C to 650C of which the average rate should be 35 to 10C per minute.

An example ofa proper cooling rate which is realized during the furnace confilgiibesis shown in FTG 3.

According to an alternative method of producing the magnet material of the invention, the mixed ingredient metals are melted at a temperature higher than 1,200C, said melt is quenched to room temperature, for instance, in a metal mold cooled by a cooling means such as water, the quenched alloy is aged at a temperature of 400 to 650C for 20 minutes to 10 hours, and then the aged alloy is cooled to room temperature.

The qunch e d alloy exhibits a low c o ercive force value such as about 200 Oe. The coercive force, however, increases to value as high as 1,250 Oe during the aging period of 1 to 5 hours at a temperature of 400 to 650C. An aging treatment below 400C requires too prolonged a period to obtain a sufficiently high coercive force value. In some cases. for a higher aging temperature, for example of 700C, the coercive force value decreases.

' Illustrative embodiments of the invention are as follows:

EXAMPLE 1 The alloy of 16.67 mol percent of Ce-mischmetal, 75.0 mol percent of Co and 8.33 mol percent of Cu was melted at 1,670C, maintained for 30 minutes at 1,000C, cooled to 400C according to the cooling curve shown in FIG. 3 and then rapidly cooled to room temperature. A sphere of about 3 mm in diameter was prepared frEjni tlie ingot. The demagnetizationcurve was measured by means of a conventinal vibrating specimen magnetometer. The magnetic properties were:

Br 6,250 G (Bl-l)max 3.3 MG Oe EXAMPLE 2 The alloy of 17.4 mol percent of Ce-mischmetal, 70.2 mol percent of Co and 12.4 mol percent of Cu was melted at 1,670C, maintained for 30 minutes at 1,000C, cooled to 400C according to the cooling curve shown in FIG. 3 and then rapidly cooled to room temperature. A sphere of about 3 mm in diameter was prepared from the ingot. The demagnetization curve was measured by means of a conventional vibrating specimen magnetometer. The magnetic properties were:

Br 5,960 G bHc 3,240 Oe (BH)max 8.0 MG'Oe EXAMPLE 3 The alloy of 16.67 mol percent of Ce-mischmetal, 66.7 mol percent of Co and 16.63 mol percent of Cu was melted at l,670C, maintained for 30 minutes at 1,000C, cooled to 400C according to the cooling curve shown in FIG. 3 and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 4,750 G bHc 2,900 Oe (BH)max 5.0 MG'Oe EXAMPLE 4 EXAMPLE 5 The alloy of 15.25 mol percent of Ce-mischmetal, 67.8 mol percent of Co and 16.95 mol percent of Cu was melted at 1,670C, maintained for 30 minutes at 1,000C, cooled to 400C according to the cooling curve shown in FIG. 3 and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 4,250 G bHc 1,200 Oe (BH)max 3.4 MG'Oe EXAMPLE 6 The alloy of 16.67 mol percent of Ce-mischmetal, 66.7 mol percent of Co and 16.63 mol percent of Cu was melted at 1,670C, maintained for 30 minutes at 1,000C, cooled to 400C according to the cooling curve shown in FIG. 3 and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 4,750 G bHc 2,900 Oe (BH)max 5.0 MG'Oe EXAMPLE 7 The alloy of 19.35 mol percent of Ce-mischmetal, 64.52 mol percent of Co and 16.13 mol percent of Cu was melted at 1,670C, maintained for 30 minutes at 1,000C, cooled to 400C according to the cooling curve shown in FIG. 3 and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 3,600 G bHc 750 Oe (BH)max 1.7 MG'Oe The influence of the Ce-mischmetal content in the Ce-mischmetal-Co-Cu alloy system is shown explicitly from the preceding three examples.

EXAMPLES 8 The alloy of 16.67 mol percent of Ce-mischmetal, 66.7 mol percent of Co and 16.63 mol percent of Cu was melted at 1,550C, maintained for 30 minutes at 1,000C, cooled to 300C according to the cooling curve shown in FIG. 3 and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 4,300 G bHc 2,750 Oe (BH)max 3.8 MG-Oe EXAMPLE 9 The alloy of 16.67 mol percent of Ce-mischmetal, 66.7 mol percent of Co and 16.63 mol percent of Cu was melted at 1,550C, maintained for 30 minutes at 1,000C, cooled to 400C according to the cooling curve shown in FIG. 3 and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 4,750 G bHc 2,900 Oe (BH)max 5.0 MG-Oe EXAMPLE 10 The alloy of 16.67 mol percent of Ce-mischmetal, 66.67 mol percent of Co and 16.63 mol percent of Cu was melted at 1,550C, maintained for 30 minutes at 1,000C, cooled to 530C according to the cooling curve shown in FIG. 3 and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 5,050 G bHc 2,730 Oe (BH)max 5.8 MG-Oe EXAMPLE 1 1 The alloy of 16.67 mol percent of Ce-mischmetal, 66.7 mol percent of Co and 16.63 mol percent of Cu was melted at 1,550C, maintained for 30 minutes at 1,000C, cooled to 600C according to the cooling curve shown in FIG. 3 and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 5,050 G bHc 2,000 Oe (BH)max 4.3 MG'Oe EXAMPLE 12 The alloy of 16.67 mol percent of Ce-mischmetal, 66.7 mol percent of Co and 16.63 mol percent of Cu was melted at 1,550C, maintained for 30 minutes at 1,000C, cooled to 790C according to the cooling curve shown in FIG. 3 and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 4,650 G bHc 150 Oe (BH)max 0.25 MG'Oe It is apparent from the preceding five examples that the temperature at which the sample is taken out from the electric furnace influences explicitly the magnetic properties.

EXAMPLE 13 The alloy of 17.4 mol percent of Ce, 66.1 mol percent of Co and 16.5 mol percent of Cu was melted at 1,550C, maintained for 30 minutes at 1,000C, cooled to 400C at the average rate of 28C/min. between 1,000C and 650C and at the overall rate of l6.5C/min. and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 4.550 G bHc 800 Oe (BH)max 2.4 MG'Oe EXAMPLE 14 EXAMPLE 15 The alloy of 17.4 mol percent of Ce, 66.1 mol percent of Co and 16.5 mol percent of Cu was melted at 1,550C, maintained for 30 minutes at 1,000C, cooled to 400C at the average cooling rate of l9.5C/min. between 1,000C and 650C and at the overall average rate of l0.5C/min. and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 6,050 G bHc 2,570 Oe (BH)max 7.1 MG'Oe EXAMPLE 16 The alloy of 17.4 mol percent of Ce. 66.1 mol percent of Co and 16.5 mol percent of Cu was melted at 1.550C. maintained for 30 minutes at 1,000C, cooled to 400C at an average cooling rate of 12C/min. between l,000C and 650C and at the overall average rate of 4C/min. and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 6,500 G bHc 900 Oe (BH)max 1.6 MG-Oe It is apparent from the preceding four examples that cooling rate influences the magnetic properties of the materials.

EXAMPLE 17 The alloy of 18.03 mol percent of Ce-mischmetal, 55.32 mol percent of Co and 26.65 mol percent of Cu was melted at 1,550C, and quenched in water. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 2,300 G bHc 260 Oe EXAMPLE 1 8 The alloy of 18.03 mol percent of Ce-mischmetal, 55.32 mol percent of Co and 26.65 mol percent of Cu was melted at 1,550C, quenched in water, aged for 1 hour at 300C and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 2,600 G bHc 490 Oe EXAMPLE 19 The alloy of 18.03 mol percent of Ce-mischmetal, 55.32 mol percent of Co and 26.65 mol percent of Cu was melted at 1,550C, quenched in water, aged for 1 hour at 400C and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 2,900 G bHc 890 Oe EXAMPLE 20 The alloy of 18.03 mol percent of Ce-mischmetal, 55.32 mol percent of Co and 26.65 mol percent of Cu was melted at 1,550C, quenched in water, aged for 1 hour at 520C and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 3,000 G bHc 1,250 Oe EXAMPLE 2] The alloy of 18.03 mol percent of Ce-mischmetal, 55.32 mol percent of Co and 26.65 mol percent of Cu was melted at 1,550C, quenched into water, aged for 1 hour at 600C and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 3,000 G bl-lc 970 Oe EXAMPLE 22 The alloy of 18.03 mol percent of Ce-mischmetal, 55.52 mol percent of Co and 26.65 mol percent of Cu was melted at 1,550C, quenched in water, aged for 1 hour at 700C and then rapidly cooled to room temperature. The measurement of magnetic properties was carried out by the same method as in the previous examples. The magnetic properties were:

Br 2,500 G bHc 260 Oe The influence of aging temperature is explicitly confirmed from the six preceding examples.

EXAMPLE 23 The alloy of 18.03 mol percent Ce-mischmetal, 55,32 mol percent of Co and 26.65 mol percent of Cu which was prepared by melting the ingredient metals at 1,550C and quenching in water, was heated at 520C for various times. The intrinsic coercive force ,H of thus-obtained alloy is plotted against the aging time in FIG. 4.

The intrinsic coercive force increased rapidly with increasing the aging time in the range from about 20 min. to 1 hour, and was followed by a gradual increase up to the aging time of about 8 hours, then by a gradual decrease with the aging time over 10 hours.

What is claimed is:

l. A permanent magnet comprising a composition of matter which consists essentially of to mol percent of at least one member selected from the group consisting of Ce and Ce-mischmetal, 52 to 77 mol percent of Co, and 8 to 30 mol percent of Cu, characterized in that the said magnet consists essentially of an as-cast body, the energy product of which is at least 1.3 million oersted-gauss.

2. A magnetic composition according to claim 1 consisting essentially of an alloy of 15.25 mol percent cerium mischmetal, 67.8 'mol percent C0 and 16.95 mol percent Cu.

3. A permanent magnet according to claim 1 wherein said member is Ce.

4. A permanent magnet according to claim 3 wherein said alloy consists essentially of 17.1 to 17.43 mol percent of Ce, 64 to 72.6 mol percent of Co and 10.3 to 18.57 mol percent of Cu.

5. A permanent magnet according to claim 1 wherein said member is Ce-mischmetal.

6. A permanent magnet according to claim 5 wherein said alloy consists essentially of 17.1 to 17.43 mol percent of Ce-mischmetal, 64 to 72.6 mol percent of Co and 10.3 to 18.57 mol percent of Cu. 

2. A magnetic composition according to claim 1 consisting essentially of an alloy of 15.25 mol percent cerium mischmetal, 67.8 mol percent Co and 16.95 mol percent Cu.
 3. A permanent magnet according to claim 1 wherein said member is Ce.
 4. A permanent magnet according to claim 3 wherein said alloy consists essentially of 17.1 to 17.43 mol percent of Ce, 64 to 72.6 mol percent of Co and 10.3 to 18.57 mol percent of Cu.
 5. A permanent magnet according to claim 1 wherein said member is Ce-mischmetal.
 6. A permanent magnet according to claim 5 wherein said alloy consists essentially of 17.1 to 17.43 mol percent of Ce-mischmetal, 64 to 72.6 mol percent of Co and 10.3 to 18.57 mol percent of Cu. 